Lead free glass frit powder for manufacturing silicon solar cell, its producing method, metal paste composition containing the same and silicon solar cell

ABSTRACT

Disclosed are lead free glass frit powder for manufacturing a silicon solar cell, its producing method, a metal paste composition containing the same and a silicon solar cell. The lead free glass frit powder for manufacturing a silicon solar cell includes Bi 2 O 3 ; B 2 O 3 ; and any one metal oxide selected from the group consisting of ZnO, Al 2 O 3  and BaCO 3 , or mixtures thereof. The glass frit powder is free of lead, and thus, it is environmental friendly. A front electrode of a solar cell formed using the glass frit powder has low resistance against contact with a substrate and high adhesion to the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lead free glass frit powder formanufacturing a silicon solar cell, its producing method, a metal pastecomposition comprising the same and a silicon solar cell, and inparticular, to lead free glass frit powder for manufacturing a siliconsolar cell, which is environmental friendly and improves the performanceof a solar cell, its producing method, a metal paste compositioncomprising the same and a silicon solar cell.

2. Description of the Related Art

Recently, it is expected that conventional energy sources such as oil orcharcoal will be exhausted, and thus interests in alternative energysource are increasing. Among alternative energy source, a solar cell hasabundant energy sources and does not cause environmental pollution, andthus it becomes the object of attention.

The solar cell is classified into a solar heat cell that produces vaporrequired to run a turbine using solar heat, and a solar light cell thatconverts photons into electrical energy using properties of asemiconductor. Generally, the solar light cell is represented as a solarcell.

The solar cell largely includes a silicon solar cell, a compoundsemiconductor solar cell and a tandem solar cell according to rawmaterial. Among them, the silicon solar cell leads the solar cellmarket.

FIG. 1 is a schematic cross-sectional view illustrating a basicstructure of a silicon solar cell. Referring to FIG. 1, the siliconsolar cell includes a substrate 101 of a p-type silicon semiconductor,and an emitter layer 102 of an n-type silicon semiconductor. A p-njunction is formed at an interface between the substrate 101 and theemitter layer 102 in the similar way to a diode.

When light falls on a solar cell of the above-mentioned structure,electrons and electron holes create in a silicon semiconductor dopedwith an impurity by the photovoltaic effect. Specifically, electronscreate in the emitter layer 102 of an n-type silicon semiconductor as aplurality of carriers, and electron holes create in the substrate 101 ofa p-type silicon semiconductor as a plurality of carriers. The electronsand electron holes created by the photovoltaic effect are drawn towardthe n-type silicon semiconductor and p-type silicon semiconductor, andmove to a front electrode 103 on the emitter layer 102 and a rearelectrode 104 below the substrate 101, respectively. When the frontelectrode 103 and the rear electrode 104 are connected to each other,electrical current flows.

A front electrode of a silicon solar cell is formed through an interfacereaction between a metal paste for forming a front electrode and ananti-reflection film. Specifically, while silver contained in a metalpaste becomes liquid at high temperature and then is recrystallized intoa solid again, a front electrode is contacted with an emitter layer dueto a punch-through phenomenon that the front electrode penetratesthrough an anti-reflection film through the medium of glass frit powder.The definite mechanism is disclosed in J. Hoomstra, et al., 31st IEEEPVSC Florida 2005.

The glass frit powder carries out an interface reaction with ananti-reflection film to etch the anti-reflection film. This is anoxidation-reduction reaction that a portion of elements is reduced andgenerated as a by-product. Conventionally, because glass frit powdercontains lead oxide (PbO) as a main component, lead is reduced after aninterface reaction and it causes environmental problems.

To solve this drawback, lead free glass frit powder containing bismuthoxide (Bi₂O₃) instead of lead oxide has been introduced. However, thebismuth oxide-based glass frit powder has lower contact resistancebetween an electrode and a substrate than conventional glass frit powdercontaining lead oxide.

Therefore, there is an urgent need for glass frit powder that is moreenvironmentally friendly and can be used to manufacture solar cells ofbetter performance than the conventional glass frit powder.

SUMMARY OF THE INVENTION

The present invention is designed to solve the problems of the priorart, and therefore it is an object of the present invention to providelead free glass frit powder for manufacturing a silicon solar cell,which is capable of manufacturing a solar cell with lower contactresistance and higher contact strength between a substrate and anelectrode than conventional glass frit powder, its producing method, ametal paste composition comprising the same and a silicon solar cell.

To achieve the object, lead free glass frit powder for manufacturing asilicon solar cell according to the present invention comprises Bi₂O₃;B₂O₃; and any one metal oxide selected from the group consisting of ZnO,Al₂O₃ and BaCO₃, or mixtures thereof. The glass frit powder of thepresent invention is free of lead, and consequently, it is environmentalfriendly. And, the glass frit powder comprises a specific metal oxide,so that it can improve the performance of a solar cell manufacturedusing the glass frit powder.

For example, the above-mentioned lead free glass frit powder formanufacturing a silicon solar cell according to the present inventionmay comprise 75 to 95 weight % of the Bi₂O₃, 1 to 15 weight % of theB₂O₃, and 1 to 20 weight % of any one metal oxide selected from thegroup consisting of ZnO, Al₂O₃ and BaCO₃, or mixtures thereof, howeverthe present invention is not limited in this regard.

In addition, to achieve the object, a producing method of lead freeglass frit powder for manufacturing a silicon solar cell according tothe present invention comprises (S1) preparing constituents to produceglass frit powder, including Bi₂O₃; B₂O₃; and any one metal oxideselected from the group consisting of ZnO, Al₂O₃ and BaCO₃, or mixturesthereof; (S2) melting the prepared constituents together; (S3) coolingthe melted mixture to form glass frit in a solid phase; and (S4)pulverizing the solid-phase glass frit into a powder phase.

In the producing method of the present invention, the melting process ofthe step (S2) may have a melting temperature of 900 to 1500° C., howeverthe present invention is not limited in this regard.

The above-mentioned lead free glass frit powder may be used to prepare ametal paste composition together with silver powder and an organicbinder, and the metal paste composition may be used to form a frontelectrode of a silicon solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a conventional siliconsolar cell.

FIG. 2 is an SEM (Scanning Electron Microscopy) image of glass fritpowder according to example 1 of the present invention.

FIG. 3 is a cross-sectional view of a silicon solar cell according to anembodiment of the present invention.

FIG. 4 is an SEM image of a front electrode according to example 1 ofthe present invention.

FIG. 5( a) is a view illustrating a peeling test, and FIG. 5( b) is agraph illustrating the peeling test results of front electrodesaccording to comparative example 1 and example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, glass frit powder of the present invention will bedescribed in detail according to its producing method. Prior to thedescription, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentinvention on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

First, constituents to produce glass frit powder are prepared, includingBi₂O₃; B₂O₃; and any one metal oxide selected from the group consistingof ZnO, Al₂O₃ and BaCO₃, or mixtures thereof (S1).

Bi₂O₃ reacts with an anti-reflection film at high temperature and etchesthe anti-reflection film so as to form a front electrode of a solarcell. For example, in the case that an anti-reflection film is a siliconnitride film (SiN_(x)), an interface reaction between Bi₂O₃ and theanti-reflection film occurs at high temperature as follows.

[Reaction Formula 1]

2Bi₂O₃(s,1)+3SiN_(x)(s)→4Bi(s,1)+3SiO₂(s)+N₂(g)

As seen in the reaction formula 1, when a portion of a silicon nitridefilm reacts with Bi₂O₃, the silicon nitride film is etched throughoxidation-reduction, and silver in the metal paste is recrystallized atthe etched portion to form a front electrode.

Bi₂O₃ according to the present invention is a main constituent of theglass frit powder replacing lead oxide, and thus, its content occupies amajority of the glass frit powder and may be properly selected withreference to the content of lead oxide used conventionally. For example,the content of Bi₂O₃ may be 75 to 95 weight % based on the total weightof the glass frit powder, however the present invention is not limitedin this regard. The above-mentioned content range leads to a very lowcontact resistance between a substrate and an electrode and a very highFF (Fill Factor) value.

B₂O₃ is a constituent of the glass frit powder for forming a stableglass phase. In the glass frit powder of the present invention, thecontent of B₂O₃ may be properly selected according to necessity, forexample 1 to 15 weight %, however the present invention is not limitedin this regard. The above-mentioned content range allows to maintain asufficiently low viscosity during the interface reaction.

In addition to Bi₂O₃ and B₂O₃, the glass frit powder of the presentinvention further comprises at least one metal oxide selected from thegroup consisting of ZnO, Al₂O₃ and BaCO₃. The exemplary ZnO, Al₂O₃ andBaCO₃ form a stable glass phase during an interface reaction andmaintain a low viscosity. If a glass component has a low viscosityduring an interface reaction, they increase the contact possibilitybetween Bi₂O₃ and an anti-reflection film, so that etching may occur atmore areas. As mentioned above, if etching occurs at relatively moreareas, a front electrode formed by recrystallization of silver has awider area, and consequently, contact resistance between a substrate andan electrode becomes lower than conventional glass frit powder,resulting in better performance of a solar cell, and contact strengthbetween a substrate and an electrode is improved.

In the glass frit powder of the present invention, the content of anyone metal oxide selected from the group consisting of ZnO, Al₂O₃ andBaCO₃ or mixtures thereof may be properly selected through repetitiveexperiments according to purpose of use and aim of a solar cell. Forexample, the content may be 1 to 20 weight %, however the presentinvention is not limited in this regard. The above-mentioned contentrange allows to maintain a sufficiently low viscosity during aninterface reaction and to ensure a very low contact resistance and avery high contact strength between a substrate and a front electrode.

Typically, in addition to the above-mentioned constituents, glass fritpowder may further comprise, for example, SiO₂, however the presentinvention is not limited in this regard.

As mentioned above, after the constituents of the glass frit powder ofthe present invention are prepared, the constituents are melted together(S2).

When the constituents of the glass frit powder are melted together underatmospheric pressure, a bond between molecules in each constituent isbroken, and consequently, each constituent loses the properties as metaloxide. Each constituent is uniformly mixed in the melted state, andwholly obtains the properties of hyaline through a subsequent coolingprocess.

In the melting process of the present invention, the present inventionis not limited to a specific melting temperature if it can melt allconstituents. For example, the melting temperature may be 900 to 1500°C., however the present invention is not limited in this regard. Theabove-mentioned constituents can be sufficiently melted at theabove-mentioned temperature range.

The present invention is not limited to a specific melting time, duringwhich the above-mentioned melting temperature is maintained, if it cansufficiently melt all constituents. For example, the melting time may be10 minutes to 1 hour, however the present invention is not limited inthis regard. Each constituent can be sufficiently melted in theabove-mentioned time range. If the melting temperature or melting timeexceeds the above-mentioned range, additional melting effects cannot beexpected.

Subsequently, the melted mixture is cooled to form a glass frit in asolid phase (S3).

The melted constituents are cured through a cooling process to form aglass frit in a solid phase. The cooling rate may be properly selectedaccording to the kind of constituents of a glass frit, however it isgenerally preferable to cool the constituents at a high rate. Thedefinite cooling conditions may be determined with reference to thephase diagram of each constituent. For example, the melted mixture maybe cooled down to 25 to 50° C. under atmospheric pressure for 1 to 5minutes, however the present invention is not limited in this regard. Ifthe cooling rate does not satisfy the above-mentioned range,crystallization occurs during cooling, thereby failing to form a glassphase.

Typical methods in the art may be used without limit to accomplish theabove-mentioned cooling rate. For example, the melted mixture may beextruded in plate form to increase the surface area or may be dippedinto water, however the present invention is not limited in this regard.

Next, the solid-phase glass frit is pulverized into a powder phase (S4).

The solid-phase glass frit has too large volume to be mixed in a metalpaste, and accordingly it is preferable to pulverize the solid-phaseglass frit into a powder phase. After pulverization, an average particlesize of the powder may be that of conventional glass frit powder in theart, for example 1 to 10 μm (micrometer), however the present inventionis not limited in this regard. The above-mentioned average particle sizerange allows a relatively uniform dispersion in a metal paste, therebybringing about an interface reaction very effectively.

Typical methods in the art may be used without limit to pulverize thesolid-phase glass frit after cooling into a powder phase. For effectivepulverization, a two-step method may be used. In this case, the samepulverizing step may be repeated twice. Alternatively, a firstpulverizing step and a second pulverizing step may be performed, whereinthe first pulverizing step is coarse pulverization and the secondpulverizing step is fine pulverization. Here, the coarse pulverizationis not limited to pulverization of the solid-phase glass frit into apowder phase of a specific average particle size, but pulverization intoa powder phase of a proper average particle size for easy finepulverization using a fine pulverization method. And, the finepulverization is pulverization of the coarsely pulverized glass fritinto powder of a desired average particle size.

And, the pulverizing process may be selected from dry pulverization orwet pulverization according to necessity. In the case of wetpulverization, water or ethanol may be added, as well known in the art,however the present invention is not limited in this regard.

FIG. 2 is an SEM image of glass frit powder according to an example ofthe present invention.

The glass frit powder produced by the above-mentioned producing methodmay be included in a metal paste composition for forming a frontelectrode of a silicon solar cell. The metal paste composition of thepresent invention comprises the above-mentioned glass frit powder,silver powder and an organic binder.

A mixing ratio of the glass frit power and the silver powder may beproperly selected depending on the manufacturing conditions. Forexample, the glass frit power may be included at an amount of 1 to 20parts by weight based on 100 parts by weight of the silver powder. Whenthe content of the glass frit powder is within the above-mentionedrange, an interface reaction sufficiently occurs and an excessiveinterface reaction is suppressed, thereby preventing junction breakdownin a solar cell.

The organic binder makes the glass frit powder and the silver powderinto a paste phase. The resulting mixture is agitated to be uniformlydispersed.

The present invention is not limited to a specific organic binder if itis used typically in the art to prepare a metal paste composition forforming a front electrode of a solar cell. For example, the organicbinder may be ay one selected from the group consisting of cellulose,butyl carbitol and terpineol, or mixtures thereof, however the presentinvention is not limited in this regard.

Here, the content of the organic binder may be properly selecteddepending on the manufacturing conditions. For example, the organicbinder may be included at an amount of 5 to 30 parts by weight based on100 parts by weight of the silver powder in the paste. Theabove-mentioned content range of the organic binder allows a suitableviscosity for screen printing and a suitable aspect ratio obtained bypreventing overflow of the paste after screen printing.

Through the above-mentioned process, a metal paste composition forforming a front electrode of a silicon solar cell, comprising silverpowder, glass frit powder and an organic binder, is prepared.

The present invention provides a silicon solar cell manufactured usingthe metal paste composition of the present invention.

FIG. 3 is a schematic cross-sectional view of a silicon solar cellaccording to a preferred embodiment of the present invention.

Referring to FIG. 3, the silicon solar cell of the present inventioncomprises a silicon semiconductor substrate 201, an emitter layer 202formed on the substrate 201, an anti-reflection film 203 formed on theemitter layer 202, a front electrode 204 connected with an upper surfaceof the emitter layer 202 by penetrating through the anti-reflection film203, and a rear electrode 205 connected with a rear surface of thesubstrate 201.

The substrate 201 may be doped with a p-type impurity such as thirdgroup elements in the periodic table including B, Ga, In and so on, andthe emitter layer 202 may be doped with an n-type impurity such as fifthgroup elements in the periodic table including P, As, Sb and so on. Whenthe substrate 201 and the emitter layer 202 are doped with impurities ofthe opposite conductivity as mentioned above, a p-n junction is formedat an interface between the substrate 201 and the emitter layer 202.Meanwhile, a p-n junction may be formed at an interface between thesubstrate 201 doped with an n-type impurity and the emitter layer 202doped with a p-type impurity.

The anti-reflection film 203 passivates defects (for example, danglingbond) on the surface or in the bulk of the emitter layer 202 and reducesthe reflectivity of solar lights incident on a front surface of thesubstrate 201. When defects existing in the emitter layer 202 arepassivated, recombination sites of minority carriers are eliminated andan open-circuit voltage of a solar cell increases. The reduction inreflectivity of solar lights increases the amount of lights reaching ap-n junction, thereby increasing the short-circuit current of a solarcell. The increase in open-circuit voltage and short-circuit currentimproves the conversion efficiency of a solar cell as much.

For example, the anti-reflection film 203 may have a single filmstructure of any one selected from the group consisting of a siliconnitride film, a silicon nitride film containing hydrogen, a siliconoxide film, a silicon oxidized nitride film, MgF₂, ZnS, MgF₂, TiO₂ andCeO₂, or a multiple film structure of at least two material films,however the present invention is not limited in this regard. Theanti-reflection film 203 may be formed by vacuum deposition, chemicalvapor deposition, spin coating, screen printing or spray coating.However, the present invention is not limited to a specific method forforming the anti-reflection film 203.

The front electrode 204 and the rear electrode 205 are metal electrodesmade from silver and aluminum, respectively. However, the presentinvention is not limited to a specific kind of electrode material. Asilver electrode has good electrical conductivity, and an aluminumelectrode has good electrical conductivity and excellent affinity forthe substrate 201 made from a silicon semiconductor, resulting in goodbonding with the substrate 201.

The front electrode 204 and the rear electrode 205 can be formed byvarious well-known techniques, however may be preferably formed throughscreen printing. That is, the front electrode 204 is formed by screenprinting the above-mentioned paste for forming a front electrode at anarea where the front electrode 204 will be located, and thermallytreating the paste. During the thermal treatment, the front electrode204 penetrates through the anti-reflection film 203 due to apunch-through phenomenon, and is connected with the emitter layer 202.

Similarly, the rear electrode 205 is formed by printing a paste forforming a rear electrode, comprising aluminum, quartz silica, a binderand so on, on the rear surface of the substrate 201, and thermallytreating the paste. During the thermal treatment, aluminum that is oneof materials used in forming a rear electrode, diffuses through the rearsurface of the substrate 201, so that a back surface field (not shown)layer may be formed at an interface between the rear electrode 205 andthe substrate 201. The back surface field layer prevents carriers'movement to the rear surface of the substrate 201 and recombination.Prevention of carriers' recombination results in increased open-circuitvoltage and fill factor, and consequently improved conversion efficiencyof a solar cell.

The present invention is not limited to a specific process for formingthe front electrode 204 and the rear electrode 205. For example, thefront electrode 204 and the rear electrode 205 may be formed by typicalphotolithography and metal deposition other than screen printing.

Hereinafter, the present invention will be described in detail throughspecific examples. However, the description proposed herein is just apreferable example for the purpose of illustrations only, not intendedto limit the scope of the invention, so it should be understood that theexamples are provided for a more definite explanation to an ordinaryperson skilled in the art.

EXAMPLE 1

29 g of Bi₂O₃, 2 g of B₂O₃, 2 g of ZnO and 2 g of BaCO₃ were mixed, andthe mixture was melted at 1200° C. for 20 minutes. The resultant meltedproduct was extruded in plate form and cooled down to 25° C. over 5minutes. The resultant cooled product was pulverized by a pulverizer toproduce glass frit powder.

7 g of the produced glass frit powder and 40 g of silver powder weremixed and agitated uniformly, and added with 10 g of an organic binderof cellulose, butyl carbitol and terpineol at a mixing weight ratio of2:5:5, and agitating them to prepare a metal paste composition.

Using the metal paste composition, a silicon solar cell wasmanufactured, comprising an aluminum rear electrode, a p-type siliconsemiconductor substrate, an n-type emitter layer, a silicon nitride filmas an anti-reflection film and a front electrode.

EXAMPLE 2

Glass frit powder, a metal paste composition and a solar cell weremanufactured in the same way as example 1, except that 35 g of Bi₂O₃, 2g of B₂O₃, 2 g of ZnO and 1 g of Al₂O₃ were mixed.

EXAMPLE 3

Glass frit powder, a metal paste composition and a solar cell weremanufactured in the same way as example 1, except that 35 g of Bi₂O₃, 5g of B₂O₃ and 4 g of ZnO were mixed.

EXAMPLE 4

Glass frit powder, a metal paste composition and a solar cell weremanufactured in the same way as example 1, except that 35 g of Bi₂O₃, 2g of B₂O₃, 2 g of BaCO₃ and 1 g of Al₂O₃ were mixed.

EXAMPLE 5

Glass frit powder, a metal paste composition and a solar cell weremanufactured in the same way as example 1, except that 39 g of Bi₂O₃, 4g of B₂O₃ and 7 g of Al₂O₃ were mixed.

EXAMPLE 6

Glass frit powder, a metal paste composition and a solar cell weremanufactured in the same way as example 1, except that 38 g of Bi₂O₃, 7g of B₂O₃ and 5 g of BaCO₃ were mixed.

COMPARATIVE EXAMPLE 1

Glass frit powder, a metal paste composition and a solar cell weremanufactured in the same way as example 1, except that 28 g of Bi₂O₃ and2 g of SiO₂ were mixed.

The solar cells of examples 1 to 6 and comparative example 1 were testedfor FF, and the results are shown in Table 1.

TABLE 1 Example Example Example Example Example Example Comparative D 12 3 4 5 6 example 1 FF 76.0% 77.0% 75.0% 74.0% 73.0% 74.0% 65.0%

EXPERIMENT EXAMPLE

1. SEM Measurement

An SEM image of the glass frit powder of example 1 is shown in FIG. 2.It is found from FIG. 2 that the glass frit powder of example 1 hasuniformity.

FIG. 4 shows an SEM image of recrystallization of silver in a frontelectrode formed using the metal paste composition of example 1. It isfound from FIG. 4 that silver is recrystallized over a wide area.

2. Peeling Test

A peeling test (ASTM D1876) was made on the front electrodes of example1 and comparative example 1 so as to measure the adhesive strength ofthe front electrode formed according to the present invention, and theresults are shown in FIG. 5.

As shown in FIG. 5, it is found that the front electrode of example 1has excellent adhesive strength.

INDUSTRIAL APPLICABILITY

The lead-free glass frit powder for manufacturing a silicon solar cellaccording to the present invention contains bismuth oxide instead oflead oxide, and accordingly, it is more environmental friendly thanlead-based glass frit powder in a producing process or subsequent use.And, a silicon solar cell manufactured using the glass frit powder ofthe present invention has low contact resistance and high contactstrength between a substrate and an electrode, and consequentlyexcellent performance and durability.

1. Lead free glass frit powder for manufacturing a silicon solar cell,comprising: Bi₂O₃; B₂O₃; and any one metal oxide selected from the groupconsisting of ZnO, Al₂O₃ and BaCO₃, or mixtures thereof.
 2. The leadfree glass frit powder for manufacturing a silicon solar cell accordingto claim 1, wherein the glass frit powder comprises 75 to 95 weight % ofthe Bi₂O₃, 1 to 15 weight % of the B₂O₃, and 1 to 20 weight % of any onemetal oxide selected from the group consisting of ZnO, Al₂O₃ and BaCO₃,or mixtures thereof.
 3. The lead free glass frit powder formanufacturing a silicon solar cell according to claim 1, wherein theglass frit powder has an average particle size of 1 to 10 μm(micrometer).
 4. A producing method of lead free glass frit powder formanufacturing a silicon solar cell, comprising: (S1) preparingconstituents to produce glass frit powder, including Bi₂O₃; B₂O₃; andany one metal oxide selected from the group consisting of ZnO, Al₂O₃ andBaCO₃, or mixtures thereof; (S2) melting the prepared constituentstogether; (S3) cooling the melted mixture to form glass frit in a solidphase; and (S4) pulverizing the solid-phase glass frit into a powderphase.
 5. The producing method of lead free glass frit powder formanufacturing a silicon solar cell according to claim 4, wherein, in thestep (S1), the glass frit powder comprise 75 to 95 weight % of theBi₂O₃, 1 to 15 weight % of the B₂O₃, and 1 to 20 weight % of any onemetal oxide selected from the group consisting of ZnO, Al₂O₃ and BaCO₃,or mixtures thereof.
 6. The producing method of lead free glass fritpowder for manufacturing a silicon solar cell according to claim 4,wherein the melting process of the step (S2) has a melting temperatureof 900 to 1500° C.
 7. The producing method of lead free glass fritpowder for manufacturing a silicon solar cell according to claim 4,wherein the cooling process of the step (S3) has a cooling temperatureof 25 to 50° C.
 8. The producing method of lead free glass frit powderfor manufacturing a silicon solar cell according to claim 4, wherein thepulverizing process of the step (S4) is a dry or wet pulverizingprocess.
 9. The producing method of lead free glass frit powder formanufacturing a silicon solar cell according to claim 4, wherein glassfrit powder obtained by the pulverizing process of the step (S4) has anaverage particle size of 1 to 10 μm (micrometer).
 10. A metal pastecomposition for forming a front electrode of a silicon solar cell,comprising: silver powder; glass frit powder; and an organic binder,wherein the glass frit powder is defined in claim
 1. 11. The metal pastecomposition for forming a front electrode of a silicon solar cellaccording to claim 10, wherein the glass frit powder is included at anamount of 1 to 20 parts by weight based on 100 parts by weight of thesilver powder.
 12. A silicon solar cell, comprising: a siliconsemiconductor substrate; an emitter layer formed on the substrate; ananti-reflection film formed on the emitter layer; a front electrodepenetrating through the anti-reflection film and connected with theemitter layer; and a rear electrode connected with a rear surface of thesubstrate, wherein the front electrode is formed by applying the metalpaste composition defined in claim 10 on the anti-reflection film at apredetermined pattern, and sintering the metal paste composition.